Many different processes involve storage vessels to contain raw materials, finished products, bi-products, and intermediate products. Many times the storage conditions involve extremes of temperature and pressure. As part of accurate control of the process, it is desirable to know the level in the vessels and other physical properties of the materials stored therein. Many different devices have been developed to detect level and density of materials in storage vessels. One such measuring system involves the use of nuclear sources installed in wells, which are in turn mounted to the storage vessels. The wells represent an elongated space which is not in fluid communication with the contents of the vessel wherein various nuclear sources are mounted. Adjacent these sources, but outside of the vessel, are corresponding detectors which sense signals emitted by the sources. The accurate placement of sources and detectors is critical to obtaining meaningful data regarding parameters such as level in the vessel or/and physical properties of the materials within the vessel. Clearly, handling of the sources must be done very carefully to minimize exposure to the operator during installation and transport. On many occasions, the clearance available next to a well located on a vessel is limited due to obstructions by other equipment or structural members. It is therefore desirable to have a compact design for a transport enclosure for the sources so that the enclosure can be easily placed in position for insertion of the sources.
Typical installations involve the placement of sources at varying depths within the well. In the past, this has been accomplished by connecting a plurality of sources to a cable, winding the cable with the sources around a drum, and enclosing the drum in a housing. Some of the disadvantages of this type of an arrangement are that the cable with sources attached becomes large and bulky when wound around a drum, necessitating the use of larger and larger housings to transport the sources to the location of use, as well as creating difficulties in actual installation due to the size of the housing used. Another problem that springs from the use of sources permanently attached to a cable is that there is no leeway in adjustment of the relative positions of the sources. Those skilled in the art can readily appreciate that when multiple sources are connected to a cable and precise alignment is required between each source and each detector on the outside of the vessel, complications can arise in obtaining overall alignment of multiple sources and detectors. Due to the permanent attachment, no fine-tuning of the relative placement of the sources is possible. A variation of the cable arrangement, previously described, has also been developed. In this arrangement, a plurality of turnbuckles are installed in the cable so that relative positional changes between the various sources connected to the cable can be made. However, the degree of adjustment is limited. The turnbuckles must be of a fairly small size so that they can wind up on the drum for installation and removal of the sources. Again, the necessity of having all of the sources premounted to a cable, even with the use of turnbuckles, still results in a housing having significant bulk. This creates problems when access to the well on a vessel is fairly limited due to the location of other equipment, utilities, or structural obstructions.
To address the requirements for a compact transport housing for sources, the apparatus of the present invention has been developed. The apparatus of the present invention provides for separate storage of the sources and their supporting members from the mechanism of raising and lowering the sources. Additionally, a perforated belt is designed that has sufficient structural rigidity to support the weight of the sources, yet at the same time is sufficiently flexible so that it can be wound around the drum with the sources separately supported. The compact design of the belt and drum allows for a smaller housing to be used because the drum size is dramatically reduced. The apparatus features safety features to prevent loss of the sources in the well and premarked perforations in the belt for accurate placement of the sources. Several details of the invention also provide for easy adjustment of the source locations, as well as a mechanism for removing the source housing and installing a mounting housing to contain the excess belt extending beyond the well in the vessel. Those and another beneficial features of the invention will be described below in detail.